Geothermal steam processing

ABSTRACT

As geothermal steam containing contaminants such as boron, arsenic, and mercury is passed through a turbine-condenser system, the contaminants preferentially collect in the initial condensate produced from the steam. Collecting this initially-produced condensate and segregating it from the remainder of the steam being condensed ensures that condensate produced from the remainder of the steam is contaminants-lean, preferably containing the contaminants in concentrations allowing for discharge of the contaminants-lean condensate to the environment.

BACKGROUND

[0001] Geothermal brine and steam reservoirs exist in many areas of theworld and are a valuable energy resource. Some steam reservoirs yield asuperheated steam which, after treatment to remove contaminants, can beused to power a turbine connected to an electrical generator. Moreusually, the reservoir yields a geothermal brine which must be flashedto produce steam to power the turbine. After powering the turbine, theexhausted steam is condensed in either a direct contact condenser or asurface condenser (e.g., a shell-and-tube-condenser) to produce steamcondensate. The steam condensate is then, in the vast majority of cases,used as liquid water make-up to a cooling tower which provides theworking fluid (i.e., the cooling medium) for condensing steam in thecondenser.

[0002] Cooling in the cooling tower is accomplished by evaporation,which produces, as a side effect, the concentration of salts, minerals,and chemicals in the non-evaporated water. If a direct contact condenseris used, as is the case with most geothermal power plants, the cycles ofconcentration in the cooling tower are normally not controlled. If asurface condenser is used, such as a tube-and-shell condenser, thecooling tower is usually operated to control the concentration of saltsby maintaining the cycles of concentration within predetermined limits.This is accomplished by controlling the cooling tower blow down, i.e.,controlling the rate at which liquid water is discharged from thecooling tower system.

[0003] Depending upon the location of the geothermal power plant, thepercentage of total condensate produced in the turbine-condenser systemwhich eventually is evaporated or discharged as cooling tower blowdownis between about 70 and 95%, leaving about 5 to 30% of excess condensatefor disposal, e.g., discharge to the environment (i.e., by distributionupon a natural earth surface or by discharge to a water body, such as alake, creek, river, or ocean). Ideally, where possible, theenvironmental discharge can also serve a beneficial purpose, e.g.,agricultural irrigation. Alternatively, the excess condensate can beused for other beneficial purposes, e.g., industrial water.Alternatively again, the excess condensate can be re-injected into thegeothermal resource formation, and in many cases this is desired tomaintain the resource pressure and volume. However, in other cases, itis not desired, but becomes a necessity because the condensate containsone or more components in excess of applicable environmental dischargeregulations. The cost of complying with such regulations—i.e., the costto construct one or more re-injection wells and the associated surfacefacilities—is quite high, on the order of $4 million.

[0004] One component dissolved in the excess condensate which may forcethe operator of a geothermal power plant to bear the cost ofre-injection to comply with environmental regulations is boron.Geothermal brines and steam typically contain boron, and as a result thesteam condensate obtained in the condenser contains boron.

[0005] Ironically, if the boron in the condensate could be controlled tolow levels, its presence would actually be beneficial. Boron is one ofsixteen important micro-nutrients needed for healthy crop growth—afactor favoring its presence in waters intended for agriculturalpurposes. On the other hand, boron in forms concentrated above themicronutrient level can inhibit starch formation and in yet higherconcentrations prove toxic to plants. The Water Encyclopedia, SecondEdition, by van der Leeden et al., Lewis Publishers, Inc. (1990), hereinincorporated by reference in its entirety, specifies in Table 6-46 a 0.5mg/l concentration as the “threshold level” below which theconcentration “should be satisfactory for almost all crops and almostany arable soil.” The “limiting concentration,” “at which the yield ofhigh-value crops might be reduced drastically, or at which an irrigatormight be forced to less valuable crops” is identified as 2.0 mg/l. Theselimits are consistent with the data in Table 6-49 of van der Leeden etal. wherein the “permissible limits” for boron are broken down by cropgroup. For those most tolerant to boron, e.g., onion, asparagus, anddate palm, the permissible limits are between 2 and 3 mg/l. Forsemi-tolerant crops, such as sunflower, potato, wheat, corn and limabean, the permissible limits are between 1.33 and 2 mg/l. And for themost sensitive crops, such as pecans, plum, apple, and most especiallycitrus and avocado, the permissible limits are from 0.67 to 1mg/l—values which are very much in line with the proposed 0.6 to 1 mg/llimits proposed for Federal drinking water regulations. See “An Updateof the Federal Drinking Water Regs,” by Pontius, Journal AWWA, February,1995, herein incorporated by reference in its entirety.

[0006] Due to the sensitivity of many crops to the presence of boron,the boron concentration in water used for agricultural purposes oftenmust comply with local water quality regulations. Citrus are among themost sensitive receptors to boron and are adversely affected at a levelof 0.75 mg/1—the limit for irrigation water in the Philippines. See inparticular pages 4468 and 4473 of the NPCC Rules and Regulations,Official Gazette, Vol. 74, No. 23, pp. 4467-4476, (1978) hereinincorporated by reference in its entirety. In addition, the Philippines,per the Ministry, Bureau and Office Administrative Orders andRegulations, Official Gazette, Vol. 78, No. 1, pp. 52-54, which documentis herein incorporated by reference in its entirety, set a 2 mg/l limiton boron for discharge to certain inland waters. The U.S. effluentstandard is also 2.0 mg/l, per the 1978 Effluent Standards of theNational Pollution Control Commission, herein incorporated by referencein its entirety.

[0007] Where no local regulations exist for boron in irrigation water,it would stand to reason that any water supplied or sold for irrigationobviously should not contain boron in a concentration greater than thetoxicity level for the plant under cultivation. For example, 2 mg/lboron in water is harmful for rice growth. Hence, to be on the safeside, the boron concentration for waters supplied to rice fields shouldbe no greater than 2 mg/l.

[0008] In light of the foregoing, it can be seen that condensateproduced from boron-containing geothermal steam poses a difficulty forgeothermal plant operations. The boron originally present in thegeothermal steam and/or in the steam flashed from the brine, ultimately,after passage through the turbine, becomes a component of the liquidsteam condensate. The boron concentration in the steam condensate isoftentimes far in excess of the 2 mg/l limit, requiring as a practicalconsequence that neither water directly taken from the condenser norfrom cooling tower blowdown be used for high value agricultural purposesor discharged into rivers, streams, and the like. Both the condensateand the cooling tower blowdown must eventually be re-injected into theearth for environmental protection.

[0009] Another problem with boron relates to cooling tower “drift”—i.e.,the moisture carried from the cooling tower into the air. If themoisture emitted from the cooling tower contains boron, say in aconcentration of 2 mg/l or more, its ultimate deposition upon the groundcan cause plant distress or death in the immediate vicinity—depending onthe sensitivity of the local plants to boron. This “drift” problem isespecially acute with respect to geothermal power plants processingsuperheated steam taken directly from the geothermal formation. As suchformations become depleted, the boron concentration in the steamproduced increases, resulting in increased boron concentration in thedrift. In particularly acute situations the boron concentration in thedrift can be exceedingly high—on the order of 100-250 mg/l—due to acombination of high boron in the steam condensate make-up and a coolingtower run with high cycles of concentration.

[0010] Besides boron, another contaminant in geothermal steam which canaccumulate in the condensate in undesirable concentrations forirrigation purposes or for discharge to inland waters or to theenvironment in general (e.g., by distribution upon the soil) is arsenic.Arsenic generally does not present as pervasive a problem for geothermaloperations as boron since its concentration in geothermal steam isusually low, as is its concentration in the resulting steam condensate.Nevertheless, there are instances where the geothermal steam can containarsenic in unusually large concentrations to produce a condensatecontaining arsenic in a concentration too high for discharge per localregulations. Generally, a limit of 0.1 mg/l will pertain for dischargeto the environment, and 0.05 mg/l is the usual maximum for drinkingwater, although Pontius reports that values in the range of 0.002 to0.020 mg/l for drinking water were under consideration in the U.S. in1995. Plant toxicity to arsenic varies widely, van der Leeden et al.indicating that the tolerance varies from as much as 12 mg/l for Sudangrass to less than 0.05 mg/l for rice. Perhaps because rice cultivationis an important agricultural activity in the Philippines, the maximumvalue permitted for irrigation is 0.01 mg/l, per the Philippines NPCCRules and Regulations of 1978 set forth hereinbefore. These sameregulations, however, set a maximum limit of 0.05 mg/l for most otherfresh surface waters, including water used as the source of public watersupply.

[0011] Another contaminant in geothermal steam which on occasion can befound to accumulate in unacceptable concentrations in the steamcondensate produced in the condenser is mercury. Mercury presentssimilar difficulties in processing as discussed above with respect toboron, except that both mercury and arsenic are seldom present insufficient concentration in the geothermal steam to cause a “drift”problem with respect to the surrounding neighborhood of the coolingtower.

SUMMARY OF THE INVENTION

[0012] It has been discovered in this invention that, as water condensesfrom steam in a condensing zone, as for example during passage through aturbine/condenser system in a geothermal power plant, contaminants suchas boron, arsenic, and mercury are preferentially removed from the steamphase with the first liquid condensed. Hence, in the invention, asubstantial proportion of one or more of such contaminants is capturedin a contaminants-rich condensate produced at an early stage of steamcondensation in the condensing zone while separately producing acontaminants-lean condensate from a later stage of condensation.

[0013] The present invention provides a method especially useful in ageothermal power plant processing steam containing boron, arsenic,and/or mercury through a turbine-condenser system. In particular, theinvention provides a method for substantially reducing the concentrationof these contaminants in the steam condensate in the condenser of ageothermal power plant processing boron, arsenic, and/ormercury-contaminated steam by capturing a substantial proportion of oneor more of these contaminants in a contaminant-rich fraction of steamcondensate produced at an early stage of condensation in theturbine-condenser system. Preferably, enough of the contaminants arecollected in this early produced fraction of steam condensate such thata later-produced fraction is contaminant-lean, containing thecontaminants in individual concentrations suitable for beneficial use inagriculture or for discharge to a naturally occurring water body.

[0014] One specific method contemplated in the invention for removingthese contaminants from a turbine-condenser system is by directing steamcontaining moisture produced in the turbine via the turbine drains to asteam/water separator operating subatmospherically. The moisture, richin the contaminants but oxygen free, is collected either as a liquid fordisposal or for such purposes as water sealing while the separatedsteam, lean in contaminants, is directed to the condenser.

[0015] Another specific method involves (1) extracting one or morestreams of steam/moisture mixtures from an interstage location in theturbine, (2) demisting the steam to produce an oxygen-free,contaminant-rich water and a demisted steam, and then (3) directing thedemisted steam to an ejector drawing non-condensable gases from the maincondenser for condensing steam from the turbine exhaust.

[0016] In addition, the invention provides for enhancing the removal ofboron, arsenic, mercury, and other contaminants from geothermal steam byscrubbing the steam prior to entry into the turbine using an aqueousalkaline liquid absorbent.

[0017] Further still, the invention provides a method for collectingmoisture in the turbine exhaust between the turbine and the condenser,which for purposes herein includes the general area of the entryway intothe condenser. The collected moisture, being oxygen-free, is then auseful liquid for use in many locations in the geothermal power plant.

[0018] The invention also provides a method, particularly applicable forlowering maintenance costs in operating a cooling tower associated witha power facility introducing an ammonia- and/or hydrogensulfide-containing steam through a turbine-condenser system, wherein atleast some of the ammonia or hydrogen sulfide is captured in an earlyproduced fraction of the total condensate produced in saidturbine-condenser system while a later produced fraction of lowerammonia or hydrogen sulfide content is used as make-up to the coolingtower. Since both ammonia and hydrogen sulfide are nutrients formicroorganisms, lowering the rate at which such nutrients are introducedinto the cooling tower system slows the growth rate of suchmicroorganisms, which in turn lowers the rate at which biocide (and itsattendant costs) must be fed to the cooling tower system to reducefouling thereof. Maintenance costs are also reduced resulting from thelonger time spans between outages necessitated for cleaning of thecooling tower system.

BRIEF DESCRIPTION OF THE DRAWING

[0019]FIG. 1 of the drawing shows a process flowsheet of the relevantportions of a geothermal power plant processing acontaminants-containing steam through a condensing zone, i.e., aturbine-condenser system, in accordance with methods of the presentinvention.

[0020]FIG. 2 of the drawing shows a four stage low pressure turbineuseful in a geothermal power plant processing contaminants-containingsteam, the turbine having means associated therewith for collectingcontaminants-rich moisture forming in the turbine as a liquidcondensate.

[0021]FIG. 3 is a graph plotting, for a boron-containing saturated steaminitially at 325° F. processed through a typical five stage low pressuregeothermal turbine, the fraction of boron in the moisture to the totalboron introduced into the condensing zone as a function of temperaturedecrease caused by the expansion of the steam.

[0022]FIG. 4 shows in cross-section an entryway into a geothermalcondenser, the entryway being designed to enhance the capture ofcontaminants-containing liquids in steam passing through the entrywayinto the main portion of the condenser.

[0023]FIG. 5 shows in cross-section yet another entryway into ageothermal condenser designed in accordance with the invention toenhance the capture of contaminants-containing liquids in steam passingthrough the entryway into the main portion of the condenser.

[0024]FIG. 6 is a schematic diagram of a shell-and-tube condenserdesigned in accordance with the invention to produce fromcontaminants-containing steam a contaminants-rich steam condensatefraction and a contaminants-lean steam condensate fraction.

[0025]FIG. 7 is a schematic diagram of a direct contact condenserdesigned in accordance with the invention to produce fromcontaminants-containing steam a first liquid stream comprising acontaminants-rich steam condensate fraction and a second liquid streamcomprising a contaminants-lean steam condensate fraction.

[0026]FIG. 8 is a schematic diagram of yet another condenser—of combinedsurface condenser and direct condenser design—to produce fromcontaminants-containing steam (a) a liquid stream comprising acontaminants-rich steam condensate fraction and (b) a contaminants-leansteam condensate fraction in accordance with the invention.

[0027]FIG. 9 is a schematic diagram of yet another condenser—of combinedsurface condenser and direct condenser design—to produce fromcontaminants-containing steam a contaminants-rich steam condensatefraction and a liquid stream comprising a contaminants-lean steamcondensate fraction in accordance with the invention.

[0028] All identical reference numerals in the figures of the drawingrefer to the same or similar elements.

[0029] It is to be understood that the drawing figures are presented inorder to facilitate an understanding of the invention. To that end, manywell known elements not needed for an understanding of the inventionhave been omitted.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention is directed in the best mode to methods forprocessing steam containing one or more contaminants selected from thegroup consisting of boron, arsenic, and mercury. For ease in describingthe invention, the discussion to follow will mainly focus on processingboron-containing steam. It is to be understood, however, that the samemethods will be applicable to processing steam containing othercontaminants such as mercury or arsenic. Moreover, it is also to beunderstood that, as used herein, the terms “boron,” “arsenic,” and“mercury” each respectively encompasses its elemental form plus allcompound forms thereof.

[0031] The present invention is founded in part on the discovery thatthe boron in boron-contaminated steam, as is the case with the typicalsteam derived from a geothermal resource, will, when liquid watercondenses from the steam in a condensing zone (as by serial passagethrough the stages of a turbine and then through a condenser), tend tocome out of the gas phase (i.e., the steam phase) and dissolve in thefirst liquid water condensed from the steam. The aim in the best mode ofthe present invention, therefore, is to process boron-contaminated steamsuch that, as liquid water is condensed from the steam, the initialliquid water condensed is collected separately from a later-condensedliquid water, with the former containing a higher concentration of boronthan the latter. In the most preferred methods, the boron concentrationin the initially-collected steam condensate will be much higher than inthe later collected steam condensate, such that the concentration in thelatter is so low that it can be used or sold for a beneficial purpose,such as irrigation or industrial water. The advantage thus offered bythe best mode of the present invention as practiced in a continuousprocess is that the bulk of the boron in the boron-contaminated steam iscaptured in one or more boron-rich liquid streams containing steamcondensate while the remainder of the steam condensate, instead ofconstituting a pollution problem requiring re-injection into the earthor subjection to a costly re-mediation process, becomes either a usefulproduct for agricultural purposes or a benign liquid for discharge tothe environment. (In some cases, the benign liquid will, but for thepresence of hydrogen sulfide, be of essentially drinking water quality.Indeed, assuming the hydrogen sulfide is removed, the steam condensatehas the advantage, as compared to typical drinking water, of beingtritium-free, and this because geothermal steam rarely if ever containstritium.) Moreover, in a geothermal power plant having a “drift” problemfrom its cooling towers, a further advantage is attained in that thepollution due to drift depositing boron in neighboring areas can beeliminated or substantially reduced.

[0032] The invention is most readily understood by reference to thedrawing. FIG. 1 shows as part of a geothermal power plant aturbine-condenser system comprising turbine 2 and condenser 6. Turbine 2is connected to an electrical power generator (not shown), and theturbine is powered by boron-contaminated steam introduced from the mainsteam supply via line 1, which steam, after passage through the turbine,exhausts by a suitable fluid communication system 101 to condenser 6.Condenser 6 may be either a surface condenser or, as is more common in ageothermal power plant, a direct contact condenser. As shown in FIG. 1,however, the condenser is a surface condenser of the tube-and-shellvariety, with cooling water from a cooling tower (not shown) beingintroduced on the tube side via line 73, traversing the tubes 100 in thecondenser, and exiting via line 75. The cooling water exchanges heatwith the turbine steam exhaust, resulting in a steam condensate (i.e.,liquid water) removed by line 85 and non-condensable gases removed byline 79.

[0033] For the geothermal power plant shown in FIG. 1, the ultimatesource of the main steam for powering turbine 2 is brine in line 102flashed to steam in high presssure flash separator 104. Alternatively,the source of the steam could be, for example, dry geothermal steamdirect from the subterranean resource, in which case the flash separatorwould not be needed. In either case, the steam is considered herein as“geothermal steam” and will typically contain boron, usually in aconcentration of about 0.1-20 ppm by weight (i.e., 0.1 to 20 lb. ofboron per 1,000,000 lb. of steam), with the boron concentrationgenerally being on the order of 5 ppm by weight. (The arsenic contentwill typically be in the range of 0.001 ppm (the analytical detectionlimit) to about 5 ppm by weight. The mercury content in geothermal steamis generally below the analytical detection limit.)

[0034] The boron-containing main steam in line 106 usually requires asteam cleaning treatment in order to remove chlorides and otherimpurities which could cause corrosion and scaling the turbine.Accordingly, if steam cleaning is necessary or desired, water or otheraqueous liquid absorbent may be added via line 108, and the water/steamadmixture directed by line 110 to steam scrubber 120. Line 110 functionsas a scrubbing zone wherein undesired constituents are absorbed into thewater or other aqueous liquid absorbent introduced via line 108.Subsequently the liquid absorbent containing the absorbed impurities isrecovered in scrubber 120 (which functions mainly as a liquid/gasseparator) via line 122. Also recovered from scrubber 120 is the cleanedsteam, which is directed by lines 124 and 1 into turbine 2.

[0035]FIG. 2 focuses more specifically on turbine 2 and depicts a fourstage low pressure turbine rotor wherein saturated boron-containinggeothermal steam is introduced via line 1 passed through the turbine1^(st) stage (nozzles 3 and rotating blades 5), then successivelythrough the 2^(nd) stage (nozzles 7 and rotating blades 9), the 3^(rd)stage (nozzles 11 and rotating blades 13), and the 4^(th) stage (nozzles15 and rotating blades 17), finally exiting the turbine and collectedfor passage to condenser 6 (shown in FIG. 1). The steam provides themotive force to spin the turbine assembly about rotating shaft 19 todrive the generator for producing electrical power. Essentially, thisinvolves a two-step transfer of energy—first from the steam to therotating turbine blades and then from the turbine to the generator toproduce electrical energy.

[0036] As the geothermal steam passes through the turbine, the processof expansion and energy extraction causes steam to initially condense inthe turbine itself in the form of moisture. For a typical geothermalsaturated steam introduced into the turbine via line 1, the moisturecontent will be about 0-1% at the entrance of the turbine and about10-15% at the exit. It is noted that the moisture content at the exit isnot necessarily indicative of the total percentage of moisture which hascondensed in the turbine because, among other considerations, somemoisture may have been removed from the turbine. Indeed, in a preferredembodiment of the invention, some of the moisture in the steam passingthrough the turbine is removed, either through the turbine drains 23,25, 27, and 29 or via one or more steam extraction lines, such as line31 leading to demister 41 (shown in FIG. 1).

[0037] As moisture forms in the turbine, boron rapidly leaves the steamphase and enters the condensed liquid moisture phase. This is showngraphically in FIG. 3 for a saturated geothermal steam at an initialturbine inlet temperature of 325° F. and pressure of about 100 psiaprocessed through a five stage low pressure (LP) turbine having no meansassociated therewith for removal of moisture prior to entry into thecondenser. Roughly 85% of the boron is absorbed into the moisture afterthe steam exits the first stage at a temperature of about 285° F. Atthis point, about 1-3%, typically about 2%, of the steam has condensedas moisture. About 95% is absorbed after the steam exits the secondstage at about 250° F., at which point about 2-6%, usually about 4%, ofthe steam has condensed as moisture. And by the time the steam exits thefifth and final stage, virtually all the boron (98%+) has collected inthe moisture, at which time about 15% of the steam has condensed asmoisture.

[0038] The foregoing values were based on processing a specifiedgeothermal steam—initially at 325° F. and of saturated quality—through aspecified turbine—i.e., a five-stage LP turbine. For geothermal steamsat other initial temperatures, pressures, and steam quality processedthrough other turbines, the results will vary, particularly as to themoisture content at various locations in the turbine. But regardless ofthe steam being treated or the turbine involved, the boron in the steampassing through the turbine preferentially collects with the first watercondensed from the steam. For a typical low pressure, low temperatureboron-containing steam passed through a typical LP turbine-condensersystem of a geothermal power plant, it is believed that about 70-90% ofthe boron will dissolve into approximately the first 5% of steamcondensed. A higher percentage, usually over 85%, and typically about90-97%, will dissolve in the first 10% of steam condensed. Virtually100% of the boron will be captured by the time the steam exits theturbine, by which time 10-15% of the steam has condensed as moisture.

[0039] From the foregoing information, it can be seen that theconcentration of boron in the water being condensed is high at theoutset, and decreases thereafter. For example, with respect to the 325°F. saturated geothermal steam exemplified above, when 85% of the borondissolves in the first 5% of moisture to condense, the boronconcentration is much higher than when 95% dissolved in 10% of themoisture, which in turn is higher than when virtually 100% of the boronwas captured in 15-20% of the moisture. Again, these values will varydepending upon the particular geothermal power plant underconsideration, particularly if ammonia is present in the steam to raisethe pH of the condensed moisture, which is believed to increase thesolubility for boron. But the two important, salient facts are that (1)a great percentage of the boron in the geothermal steam collects in themoisture formed in the turbine and (2) the concentration of the boron inthe moisture is greatest when the boron first comes out of the gas phaseand enters the moisture and progressively decreases thereafter. Thesefacts offer some flexibility in removing the boron by its capture in themoisture produced in the turbine. For example, depending on theparticular turbine-condenser system under consideration, it may bedecided to capture all the moisture produced in the turbine or, in othersituations, to capture only that portion which is highly concentrated inboron. Indeed, yet other options are possible, such as capturing themost highly concentrated moisture as one liquid stream and a portion orall of the remainder as a separate liquid stream. Exactly which optionwill be most useful for a given power plant will depend on a host offactors, such as the initial boron concentration of the steam enteringthe turbine, the concentration level to which the boron is desired ortolerable in the condensate of condenser 6, the temperature of the steamentering the turbine, the temperature at the exit of each stage, theconcentration of ammonia in the steam entering the turbine, and theability or practicability of removing moisture at various locationsalong the turbine train.

[0040] In any event, in accordance with the invention, the aim whenprocessing boron-containing steam through a turbine-condenser system isto capture some or all of the moisture produced in the turbine, orimmediately thereafter, so that a steam of reduced boron content isintroduced into the condenser (or a portion of the condenser) to producea corresponding steam condensate of reduced boron content. Statedanother way, the bulk of the boron in the steam is captured in anearly-produced boron-rich fraction(s) of the total steam condensate,which fraction(s) preferably include all of the initially producedmoisture, thereby providing for a subsequently produced boron-lean steamcondensate fraction(s) of properties so benign as not to requirere-injection into the earth. Embodiments of the invention foraccomplishing these objectives, along with a further embodiment forincreasing the efficiency of the steam scrubber 120 for removing boron,will now be explained in more detail.

[0041] Moisture, entrained in the steam as a mist as it passes throughthe turbine, is removed (as illustrated in FIG. 2) in three generallocations. Some exits the turbine with the exhaust to the condenser.Some is pushed by centrifugal force against the shell 21 of turbine 2and is collected and removed in the turbine drains, shown in FIG. 2 asfour interstage drains 23, 25, 27, and 29. The remainder is drawnthrough line 31 with steam to be used for beneficial purposes in thepower plant.

[0042] Normally, in conventional operation, water collected in theturbine drains is directed to the condenser, to mingle with the waterproduced from condensing the turbine exhaust steam. However, in oneembodiment of this invention, the boron-rich steam condensate in theturbine drains is deliberately not introduced into the condenser andindeed is kept segregated from the condensate in condenser 6. In thisembodiment, shown in FIGS. 1 and 2, the liquid/steam mixtures enteringthe four interstage drains are directed to a steam/water separator 33operating subatmospherically, from which is obtained steam relativelyfree of boron via exit pipe 35 and a stream of boron-rich water via pipe37. In this manner, a significant proportion of the boron which enteredthe turbine is captured in the liquid exiting pipe 37. Typically, over25%, usually about 35-60%, of the boron in the steam entering theturbine is collected and removed with the water leaving the turbinedrains, this water usually constituting less than 10%, often about 28%,and typically about 5% of the total steam condensate produced in theturbine/condenser system. Hence it can be seen that the invention inthis embodiment provides a method for capturing a significant amount ofboron in a relatively small stream of water while keeping the capturedboron from entering the condenser to contaminate the condensate producedtherein.

[0043] The invention provides yet another method for removing moisturehigh in boron content from the turbine-namely by drawing off steamcontaining moisture via circumferential manifold 39 (shown in FIG. 2)and directing the steam via line 31 to demister 41 (shown in FIG. 1), orother suitable liquid/vapor separator, to collect the moisture andrecover it as a stream of boronrich condensate in line 43. If desired,boron-rich condensate recovered in demister 41 may be used as the watersource for line 108 for the aqueous liquid scrubbant needed to removechlorides and other impurities, the boron-rich condensate being directedto line 108 via line 132, pump 146, and line 114, with valve 118 beingopen.

[0044] The steam relatively free of boron exiting demister 41 can beused for any convenient and appropriate beneficial use in the geothermalpower plant. Preferably, in order to increase turbine efficiency byreducing the moisture content downstream of entry of line 47 intomanifold 49, some of the steam recovered from demister 41 is superheatedand then directed to manifold 47 in a superheated condition. This can beachieved, for example, by indirect heat exchange with a hot geothermalbrine, such as the residual brine obtained after high pressure flashing.For this purpose, the steam would be directed by lines 130, 116 and 134and valve 144 to surface heat exchanger 136, there to exchange heat withbrine which enters the exchanger via line 138 and exits via line 140,the superheated steam then being directed by line 47 to an interstagelocation (downstream of manifold 39) in turbine 2. Also in the preferredembodiment, some of the steam from demister 41 is utilized as the motiveforce for a steam ejector to remove non-condensable gases from maincondenser 6. As shown in FIG. 1, to achieve this end, the steam wouldA98012US.APP 29 be directed by lines 130, 126, and 152 and valve 128 toejector 154 which directs the non-condensable gases in line 79 via line156 to ejector condenser 150 wherefrom the non-condensable gases arereleased to the atmosphere by line 160 while recovering a steamcondensate via line 161. Directing steam from turbine 2 through demister41 as in this embodiment to ejector 154 has two advantages in additionto removing boron from the turbine-condenser system: (1) the steam beingused to power the ejector is of reduced boron content, so its ultimatedischarge should present no environmental difficulties and (2) the steamcarries a considerable proportion of the non-condensable gases thatentered the turbine, so the load on ejector 150 is reduced because itneeds to remove a lower amount of non-condensable gases from condenser6.

[0045] One advantage in extracting steam from the turbine via line 31,regardless of how it is ultimately used, resides in the fact that, whilethe concentration of boron in the water condensing in the turbine isgreatest in the earliest stages of the turbine, the amount of condensateproduced in the earliest stages is relatively small, and of thatrelatively small amount, only a portion-usually only a minor portion—isrecoverable in the turbine drains. Thus, the present embodiment improvesthe efficiency of recovering boron in a relatively small fraction of thetotal condensate ultimately produced from the steam by drawing steamfrom the turbine at a location where the moisture is of a relativelyhigh boron concentration and demisting that steam in order to capturethe moisture as a boron-rich liquid stream. The percentage of boronentering the turbine which is captured by this method will vary,depending on such factors as the location where steam is drawn from theturbine to the demister, the rate at which the steam is drawn off, itsmoisture content, and the boron concentration of the moisture.Generally, when this method is employed, at least 10%, preferably atleast 20%, and most preferably at least 30% of the boron entering theturbine is captured in the demister 41 (or other liquid-vaporseparator), with the fraction of liquid condensate collected in demister41 and recovered therefrom as a boron-rich liquid usually being on theorder of 2-10%, preferably 2-6%, of the total condensate produced in theturbine-condenser system.

[0046] In an alternative embodiment of the invention, steam scrubber 120is operated with an alkaline liquid absorbent so as to enhance theremoval of boron from the main steam. Specifically, the pH of theabsorbent may be raised above 7.0, preferably to about 8-10, by using asuitable base, such as caustic or soda ash. The preferred base, however,is ammonia, since it provides the advantage that its carry-over into theturbine is innocuous and, indeed, serves as an aid to reduce stresscorrosion cracking of the turbine blades while also enhancing theremoval of boron into the moisture produced in the turbine. Morespecifically, some or all of the ammonia will dissolve into the moistureproduced in the turbine, thereby increasing its capacity for absorbingboron.

[0047] It is to be noted that the scrubber will effect some removal ofboron (and arsenic) from the steam, even if only water is the scrubbantused therein. With water alone, about 25% of the boron (and about 50% ofthe arsenic) can be removed from the steam. Depending upon the level ofboron to be tolerated in the boron-lean condensate ultimately to beremoved from the condenser 6 via line 85, the boron may presentdifficulties discussed hereinbefore when its concentration in the steamleaving the scrubber and entering the turbine is at a threshold value ofabout 0.5 ppm by weight, with increasingly higher concentrations (e.g.,above 1 ppm, above 2 ppm, above 3 ppm, above 4 ppm, etc.) causingincreasingly more serious difficulty in disposing of the steamcondensate from the condenser. (For arsenic, the troublesome thresholdvalue is about 0.01 ppm by weight, with values increasingly above thatvalue, e.g., above 0.05 ppm, above 0.1 ppm, above 0.5 ppm, etc., causingincreasingly more difficulty in disposing of the condensate. Mercury, asstated hereinbefore, is generally too low in geothermal steam to bedetected analytically, although it can sometimes be detected in thesteam condensate in troublesome values exceeding 0.002 mg/l.)

[0048] If the steam recovered from the steam scrubber in main steam line124 is superheated, one may choose to add water on a continuous basisinto the steam to increase the amount of moisture present in theturbine, which in turn provides for greater recovery of boron in liquidsrecovered therefrom, e.g., via the turbine drains or via line 31 leadingto demister 41. The water would usually be introduced into line 1 at asufficient rate to ensure that moisture is present in the steam in oneof the early turbine stages, preferably in the first stage or betweenthe first and second stages. The source of water added to the main steamfor this purpose is not critical but is preferred to be a steamcondensate. One option shown in FIG. 1 is to continuously direct intoline 1 a boron-rich, oxygen-free condensate recovered in line 132 fromdemister 41 by pump 146, lines 114 and 112, and valve 158. The preferredmethod for adding the water to the steam is by injecting water into theturbine steam chest immediately upstream of the first stage of theturbine along the outside edge of the 1^(st) stage nozzles.

[0049] In yet another embodiment, the present invention provides for theremoval of boron by collecting boron-containing moisture in the steamexiting the turbine and/or entering the condenser. In essence, anysuitable method for capturing this moisture and segregating it from theboron-lean condensate being produced in the condenser is applicable.Preferably, this is accomplished with as little additional pressure dropas practicable. One general method for carrying out this embodiment ofthe invention is to collect boron-rich water films that inherentlydevelop on the internal surfaces in the turbine exhaust area and/or inthe entrance portion of the condenser. By providing channels and drainsin appropriate locations, the water films can be directed by gravity—orby the centrifugal force in the turbine exhaust ducts—to the drains forremoval from the turbine-condenser system. In turn, these methods can beenhanced, for example, by using demister vanes to force more water tothe walls of the turbine exhaust or condenser entry or by lining thewalls, or portions thereof, with appropriate materials for collectingmore water at the walls. Among the suitable materials include shavedmetal, steel wool, and pressed or woven plastic pads, such as“Scotch-Brite” commercial scouring pads.

[0050]FIG. 4 shows an example of the foregoing methods as applied to anentryway into the condenser. In particular, FIG. 4 depicts incross-section a plenum chamber in which the steam containing moisturefrom the turbine exhaust is introduced at the top of rectangularentryway chamber 51, subsequently exiting and dividing into two streamsat the bottom. The two streams enter chambers 53 and 55, respectively,and rise to the top to exit via exit lines 57 and 59, respectively, intothe main portion of the condenser, i.e., the portion where steam iscondensed by heat exchange with a coolant fluid. Steel wool 61 ismounted internally on sidewalls 63 of entryway chamber 51, and at thebottom of chamber 51 is a liquid collection channel 65 around the innerperimeter of chamber 51. In both chambers 53 and 55 are upper and lowervanes 66 and 67 welded to the exterior of wall 63, and upper and lowervanes 68 and 69 welded to the interior of wall 70 in the case of chamber53 and wall 71 in the case of chamber 55. The vanes are mounted at anupward angle to the flow of the steam. Floor 169, having its highestpoint in the center, declines gradually to walls 70 and 71.

[0051] In operation, as steam containing boron-containing moisture isintroduced into entryway chamber 51 of the plenum chamber, the inherentfilm-forming tendency of sidewalls 63 is substantially enhanced by thepresence of the moisture-retaining property of steel wool 61, with thewater film thus created descending by gravity into collection channel65. In chambers 53 and 55 the upwardly-directed vanes increase thesurface area for liquid to collect. Moisture collecting as a film on theupper surface of upper vanes 66 and 68 collects in the channel formed bythe “V” where each vane meets its respective sidewall. Moisture formingon the lower surface of upper vanes 66 and 68 cascades as a film downthe vane and its associated sidewall to collect in the “V” of lowervanes 67 and 69, respectively. Moisture forming on the lower surface ofeach lower vane 69 cascades sequentially down its underside andassociated sidewall to the corners where the sidewalls meet floor 169,there to collect and pool with liquid from the water film forming onfloor 169 itself. In each location where pools of liquid form—channel65, the “V” of the vanes, and floor 69—the plenum is designed withdrains and associated piping (not shown) for directing the collectedliquid to a location external to the condenser. Because the boron in themoisture-containing steam entering the condenser plenum ispreferentially contained in the moisture of the steam or in the moistureforming in the plenum, the collected liquid will contain a significantproportion of the boron that entered the plenum in themoisture-containing steam. And by directing this collected liquid (whichis boron-rich water) to locations outside the condenser, the steam whichexits the plenum via pipes 57 and 59 will be of reduced boron-content sothat the resulting condensate produced from this exiting steam in themain portion of the condenser will be of reduced boron content-i.e.,reduced in comparison to what the boron content would have been withoutthe use of the boron-collecting method as described above with respectto FIG. 4.

[0052]FIG. 5 shows another condenser entryway embodiment of theinvention as could be applied to a turbine exhaust and downflow plenumfound on many commercial direct contact condensers, such as those usedat Units 1 to 6 of the Tiwi geothermal power plant in the Philippines.FIG. 5 depicts one of the two turbine exhaust diffusers 201 thatdischarge boron-containing steam into the rectangular downflow plenum 51of the condenser. Steam flows to the bottom of plenum 51 and then intothe main portion of the condenser where the steam is condensed by directcontact with a coolant liquid.

[0053] In the invention, the boron-rich moisture carried in the steam indiffuser 201 is collected in the following ways. Moisture is collectedthrough the centrifugal action of the steam through water collectinggrooves 205 in the wall of diffuser 201. Steel wool 61, mounted on theplenum sidewalls 63, retains any moisture which comes in contact withthe wall, preventing it from being stripped off, and re-entrained, bythe turbulence of the steam. Moisture collected on the walls ultimatelygathers in collection channels 65 integral with sidewalls 63 at thebottom of plenum 51. Demister vanes 207 are arranged by design tominimize pressure drop while directing more moisture to the walls andinto integral collection channels 65. More moisture is collected in themoisture-retaining pads 209, such as “Scotch-brite” pads, on the uppersurface of V-shaped drain surface 203 mounted just beneath plenum 51 butabove the liquid level of the steam-condensing portion of the condenser.The boron-rich liquid collected in the water-collection devices 65, 205,and 203 is then directed (by means not shown) through the external wallof the condenser to be kept separate and apart from the steam condensingin the main portion of the condenser. (If desired, the water collectingin grooves 205 may be separately directed, by means not shown, tocombine with the water/steam mixture in the final turbine drain line 29leading to separator 33.)

[0054] In alternative embodiments to the invention, the entire steamflow exhausting from the turbine could, prior to entry into thecondenser, be passed through a full-flow demister using vanes to directmoisture to the walls. Alternatively still, the entire flow could bedirected through structured packing of low pressure drop design. In bothsuch embodiments, as well as those depicted in FIGS. 4 and 5, the designwould include means for directing the captured moisture to a locationexternal to the condenser to be segregated from the boron-lean steamcondensate produced therein.

[0055] Yet another method for capturing boron in the steam from theturbine is by condensing in the main portion of the condenser at leasttwo separate steam condensate fractions, with the first fractionproduced having a higher boron content than any subsequently producedfraction. One such method, involving capture of the bulk of the boron inthe steam in a first fraction of steam condensate and segregating thisfraction from the remainder of the steam condensate produced, isdepicted schematically in FIG. 6. Condenser 6 in this embodiment may be,for example, a shell-and-tube type condenser in which the steam iscondensed on the shell side of the condenser while cooling water from acooling tower (or other coolant working fluid) is introduced on the tubeside via line 73 and exiting via line 75. The boron-containing steamfrom the turbine is introduced into the condenser via line 101 and iscondensed through exchange of heat with the coolant, with any remainingnon-condensable gases being removed via line 79. The condenser 6contains an appropriate barrier 81 to segregate steam condensate firstproduced from the steam entering the condenser from condensate producedthereafter. Thus, as the steam undergoes condensation, the firstfraction of the steam to condense, which will contain a high proportionof the boron which entered the condenser, is collected and segregatedfrom a second but much larger fraction containing a low proportion ofthe boron which entered the condenser. The first fraction (i.e.,boron-rich condensate) is recovered via line 83 while the remainingsecond fraction of low boron content is removed via line 85 and used forbeneficial uses, e.g., agricultural irrigation and cooling towermake-up.

[0056] The foregoing embodiment of the invention as illustrated in FIG.6 is especially useful for those geothermal power plants which introducesuperheated steam into the turbine and produce little or no moisture inthe turbine. Likewise, this embodiment is applicable when the existingturbine design cannot be modified to allow for recovery of substantialamounts of moisture directly from the turbine, as by the methodspreviously described with respect to removing moisture via the turbinedrains or by steam extraction via line 31. In such cases, due to eitherthe lack of moisture created in the turbine or the impracticality ofremoving water directly from the turbine, the process shown in FIG. 6achieves the same end result—producing one or more streams of boron-richcondensate isolated from a boron-lean condensate. In addition, it iscontemplated that the embodiment illustrated in FIG. 6 would also beuseful even when the steam to be condensed does not necessarily comefrom a steam turbine. For example, the embodiment illustrated in FIG. 6is contemplated as an especially useful design for an ejector condenseroperating with boron-containing steam as the motive force. Likewise, itwould also be a suitable choice for a binary heat absorption unit. As tothe latter, a liquid hydrocarbon or similar working fluid introduced vialine 73 would vaporize (or become superheated if it already is in vaporform) as it condenses the boron-containing geothermal steam entering byline 101. The heated hydrocarbon vapor would then exit via line 75 to besubsequently used as the motive force for a binary turbine (not shown).

[0057] A modified version of the condenser shown in FIG. 6, but of thedirect contact design instead of shell-and-tube design, is shown in FIG.7. As with the embodiment depicted in FIG. 6, steam is introduced vialine 101 into a first condensing zone wherefrom a boron-rich condensateis collected via line 83, with residual steam then passing to a secondcondensing zone on the other side of barrier 81, where it is condensedand collected as a boron-lean condensate in line 85. Coolant liquid isintroduced via lines 73 a and 73 b into the first and second condensingzones, respectively, and used as the medium for condensing steam bydirect contact. Any convenient source of water may be used for thecoolant, but, in the preferred embodiment, the coolant is derived fromtwo independent sources. The first coolant source, for line 73 a, isboron-rich, oxygen-free condensate collected upstream of condenser 6,for example, in demister 41 and/or separator 33 shown in FIG. 1. Ifnecessary, this condensate may first be cooled in order to effectivelyfunction as a coolant introduced into condenser 6. The second coolantsource, for line 73 b, is from the main cooling tower. Contact of steamand the second coolant produces a boron-lean condensate, which,contained in a condensate/second coolant mixture, is used as makeup tothe cooling tower via line 85.

[0058] The foregoing embodiment depicted in FIG. 7 may be used as ageothermal main condenser. Hence, it is shown with reference numerals inthe drawing pertaining to the main condenser. However, this embodimentis more especially contemplated as an ejector condenser for an ejector(not shown in the drawings) operating with a boron-rich steam as themotive force when a boron-lean ejector condensate containing extremelylow levels of boron—e.g., less than 0.5 mg/l, preferably essentiallyzero mg/l—is desired.

[0059] Yet another embodiment for carrying out the invention is shown inFIG. 8, which depicts condenser 6 as a “hybrid” surface-direct contactcondenser. Steam entering turbine 2 via line 1 exhausts via line 101into direct contact chamber 103 wherein the first fraction of steamentering condenser 6 is condensed. Cooling water from the cooling tower(not shown) is introduced into chamber 103 via line 73 d and also vialine 105, the latter after passage from line 73 c through the tube side100 of the shell-and-tube surface condenser in chamber 107. Wallbarriers 109, 111, 113, and 115 are provided to ensure that steamcondensed in each chamber is collected in its lower portion and keptseparate from condensate collected in the other chamber. The wallbarriers further ensure that the steam exiting from the direct contactchamber 103 must travel tortuous paths to enter the surface condenserchamber 107, with any condensate developing on both sides of barriers109 and 113 and on the right side of barriers 111 and 115 tending bygravity to collect in the condensate collected in the lower portion ofdirect condenser chamber 103 while condensate forming on the left sideof wall barriers 111 and 115 tend by gravity to collect in thecondensate collected in the lower portion of surface condenser chamber107. Inasmuch as the first fraction of the steam entering condenser 6 iscondensed in direct contact chamber 103, the condensate of this firstfraction will be boron-rich while that of the second, smaller fractioncondensed in surface condenser chamber 107 will be boron-lean. Inaddition, and importantly, whereas the boron-rich condensate will beoxygen-rich, having come in contact with, and commingling with, theoxygenated cooling tower water from lines 73 d and 105, the boron-leancondensate collected in surface condenser chamber 107 will beoxygen-free for purposes of geothermal operation. The oxygenated,boron-rich fraction of the condensate is then returned to the coolingtower via line 117, pump 119, and line 83 while the oxygen-free,boron-lean condensate is directed via line 121, pump 123, and line 85either to disposal, beneficial uses in the geothermal plant, orbeneficial purposes external thereto, i.e., irrigation or discharge tothe environment. Any non-condensable gases produced in condenser 6 arepassed via passageway 127 leading to a line 79 directed, for example, toa gas cooler or ejector (not shown) for further handling.

[0060] A noteworthy advantage of the foregoing “hybrid” embodiment, incommon with condensation performed in a surface condenser, is that, if“drift” is not a problem at the particular geothermal facility, theboron concentration in the cooling tower can be run up to high levels byallowing high cycles of concentration, thus decreasing maintenance andchemical costs as compared to operation with a direct contact condenser.

[0061] Another “hybrid” condenser in accordance with the invention isdepicted in FIG. 9. As with the embodiment shown in FIG. 7, thiscondenser, although useful as a main condenser and depicted withreference numerals pertaining thereto, is more especially contemplatedfor an ejector condenser associated with an ejector (not shown in thedrawings) operating with a boron-rich steam as the motive force when aboron-lean ejector condensate containing extremely low levels ofboron—e.g., less than 0.5 mg/l, preferably essentially zero mg/l—isdesired. The coolant, which is usually liquid from the cooling tower, isintroduced into condenser 6 via line 73, passes through cooling tubes100, and then into line 105, which, after passing through L-shaped tray125, terminates in sparger 180. Some of the boron-containing steamentering via line 101 initially condenses and collects on tray 125 as aboron-rich condensate, which is removed by line 83. The remainder of thesteam passes to the lower section of condenser 6 and therein iscondensed by direct contact with coolant introduced from sparger 180.The resulting liquid containing boron-lean condensate is removed fromthe condenser by line 85 and then used, for example, as make-up to thecooling tower. For both this embodiment, and that shown in FIG. 7, theattainment of an extremely low level of boron in the boron-leancondensate recovered in line 85 will itself depend, in great measure,upon the sources of make-up to the cooling tower introducing, overall,very little boron into the cooling tower system.

[0062] It is, of course, within the concept of the invention to combineone or more of the foregoing or equivalent methods for producing one ormore fractions of the steam condensate having a relatively highconcentration of boron, and segregating or isolating these producedfraction(s) from that portion of the condenser wherein one or moreboron-lean fractions are subsequently produced. Given the main aim forwhich the present invention is currently envisioned—producing asignificant amount of boron-lean condensate not requiring re-injectioninto the earth by capturing the bulk of the boron in an early producedfraction of the total steam condensate—all of the foregoing methods forproducing boron-rich condensate fractions can be used, usually as partof one of two overall process designs. The first design aims to capturethe bulk of the boron in one or more manageable liquid streamsconstituting a small fraction of the total condensate, thereby producinga relatively large fraction of boron-lean steam condensate to be used,for example, partially as make-up to a cooling tower system andpartially for discharge to the environment or for agricultural purposes.For this embodiment, the methods discussed hereinbefore with respect todemister 41 and the embodiments depicted in FIGS. 2, 4, 5, and 9 aremost particularly applicable, as are the embodiments shown in FIGS. 6and 7 when barrier 81 is located (as shown in the Figures) close to thesteam inlet line 101. In the second design, the boron-rich fraction willbe much the larger fraction, usually constituting over 50%, indeed,preferably over 65% or more, of the total steam condensate, with theremainder being largely the boron-lean condensate not requiringre-injection into the earth. The condenser design shown in FIG. 8 ismost particularly applicable for this method, as are the embodiments ofFIGS. 6 and 7 when barrier 81 is modified to be located a substantialdistance away from the steam inlet line 101.

[0063] While both of the two overall designs accomplish the same endresult—producing a liquid from the main condenser that does not requirere-injection into the earth, each design has distinct advantages. Theadvantage of the second design, at least for the preferred embodiment,is simplicity in disposing of the boron. More specifically, the bulk ofthe boron is ultimately directed to the cooling tower system and then,following normal practice for cooling tower blowdown, re-injected intothe earth. On the other hand, the first overall design is more usefulwhen concentrating boron in the cooling tower system is not a viableoption, for example, due to cooling tower “drift” problems, or if thecooling tower blowdown cannot be re-injected but must be disposed of onthe surface. Likewise, this second design is of advantage if, in theparticular geothermal power plant, it is deemed advantageous to captureand segregate the boron in one or more manageable boron-rich liquidstreams constituting only a small proportion of the total steamcondensate. Usually, in embodiments within this design, the boron-richliquid streams will constitute in total less than about 25%, preferablyless than 20%, more preferably less than 15%, and most preferably lessthan 10% of the total steam condensate produced in the turbine-condensersystem. Even more preferred is if such fractions constituted less than8%, more preferably less than 5%, and most preferably less than 3%, ofthe total condensate produced in the turbine-condenser system.

[0064] These fractions of boron-rich liquid streams can (as will bedetailed hereinafter) find use in a variety of ways in the geothermalpower plant. Alternatively, they may be directed to disposal (e.g., bylines 43 or 37), as by re-injection into the geothermal formation.Inasmuch as such re-injection involves only a small fraction (andpreferably only a very small fraction) of the total condensate producedin the turbine-condenser system, and since the cost of re-injectionwells is largely a function of the volumetric liquid flow rate requiredfor re-injection, the cost of such re-injection wells will besignificantly lower as compared to what would be required if all theproduced condensate not needed for cooling tower make-up had to bere-injected. And obviously, the smaller the ratio of total boron-richfractions required to be re-injected to the total condensate produced,the greater will be the cost savings involved for re-injection of theboron-rich liquid.

[0065] Regardless of which of the two overall designs is chosen, anadvantage is realized in handling the excess steam condensate not neededfor cooling tower purposes. A typical geothermal power plant ultimatelyrequires at least about 70% of the total steam condensate produced inthe turbine-condenser system for cooling tower needs (i.e., forevaporation plus blowdown). The excess steam condensate constitutes atleast about 5%, often at least 8%, and typically at least 10%, up to amaximum of about 30% of the total steam condensate yielded in theturbine-condenser system. The advantage offered in the invention is thata significant fraction (or all) of this excess steam condensate isobtained from the condenser as one or more boron-lean liquid streams notrequiring re-injection; hence a savings in the costs for re-injection.In preferred embodiments of the invention, at least 50%, more preferablyat least 65%, more preferably still at least 75%, and most preferably atleast 85% or more of the excess steam condensate is not re-injected intothe earth. Rather, it is disposed of on the earth's surface, e.g., byenvironmental discharge, and preferably to irrigate plants undercultivation.

[0066] The total of boron-rich liquid streams produced in the process ofthe invention—either containing a major proportion of the total steamcondensate in accordance with the first design described above orcontaining a minor proportion in accordance with the second—will,ideally and preferably, carry as much as possible of the boronintroduced into the turbine. (For calculation purposes herein, theamount of boron or other contaminant introduced into the turbine isdetermined immediately after the final process step (if any) forremoving impurities from the impure geothermal steam while neglectingboron introduced by recycle into the steam after that location. Thus,for the system depicted in FIG. 1, the calculated rate at which boron isintroduced into turbine 2 is the total of boron entering from line 124.Boron entering as recycle via line 112 and possibly line 47, the latteras carry-over from the demister, is not included.) At least 50%, usuallyat least 70%, and, if possible, preferably at least 80% of the boron (orother contaminant) is contained in the total of the boron-richfractions. Alternatively stated, and focusing on the boron-leancondensate produced in line 85 by the continuous process shown in FIG. 1instead of the boron-rich condensate, the boron-lean condensate isrecovered via line 85 carrying boron at a mass rate no greater than 50%,usually no more than 30%, and preferably no more than 20% of the massrate for boron entering the turbine. (These same percentages also applyfor contaminants other than boron.) For the embodiment shown in FIG. 1,wherein a surface condenser is employed for condenser 6, the foregoingpercentages would be calculated by dividing the mass rate of boroncarried in line 85 by the mass rate of boron introduced via line 124,and multiplying the result by 100. The same calculation would beinvolved for a direct contact condenser, except that the mass rate ofboron entering the condenser with the coolant would have to besubtracted from that leaving the condenser in order to determine theboron mass rate of the boron-lean condensate carried in line 85. Similarcalculations, as would be apparent to those skilled in the art, wouldapply to a hybrid condenser design.

[0067] The boron concentration in the boron-lean condensate produced inthe condenser and yielded via line 85 is reduced as compared tooperation without production and segregation of the boron-rich fractionsas described above. Normally some boron will be present in theboron-lean condensate but preferably within limits such that some of itmay safely be discharged to the environment. More specifically, it iscontemplated that, when the main aim is the release of a liquid streamfrom the condenser to the environment, the first criteria of thegeothermal operator will be to determine what maximum target level ofboron is desired for the boron-lean condensate to be removed from thecondenser for this purpose. Then, given (among other things) thecondenser design, the concentration of boron in the geothermal steamentering the turbine, the rate at which coolant from a cooling tower isused directly to condense steam in the condenser, and the concentrationof boron in such coolant, the determination to be made is how much boronmust be continuously removed in stream(s) of boron-rich condensate inorder to achieve the desired boron concentration in the boron-leancondensate. Once that determination is made, then one can take advantageof one or more of the numerous examples herein provided, and theirobvious equivalents, to capture the necessary amount of boron in liquidstreams comprising boron-rich condensate, and segregate such streamsfrom the remainder of the steam condensate.

[0068] In the preferred embodiment, the boron concentration of theboron-lean condensate (or boron-lean condensate plus coolant liquid)produced from the condenser 6 via line 85 is no greater than 2 mg/l,more preferably no greater than 1 mg/l, even more preferably no greaterthan 0.75 mg/l, and most preferably no greater than 0.5 mg/l. Assuminglevels below 0.5 mg/l can be achieved, a preferred maximum concentrationwould be 0.4 mg/l, with 0.2 mg/l and 0.1 mg/l being, respectively, morepreferred and most preferred. If arsenic is a contaminant to be capturedby the method of the invention, the arsenic content of the arsenic-leancondensate is preferably maintained below 0.10 mg/l and more preferablybelow 0.05 mg/l. Another contaminant which can be removed by the methodstaught above for boron is mercury, with the preferred mercury level inthe mercury-lean condensate being no more than 0.002 mg/l.

[0069] In the best mode of the invention, one or more of the liquidstreams comprising boron-rich condensate produced in accordance with theinvention are advantageously employed within the geothermal power plant.For example, when operating in accordance with the first of the overalldesigns described above, the boron-rich fraction(s) constituting themajority of the total steam condensate can be used as make-up to thecooling tower. The second design also offers possibilities for use (andthus avoiding re-injection) of the boron-rich fraction(s)—and thisdespite the fact that the boron-rich fraction(s) constituting a minorityof the total steam condensate will be far more concentrated in boronthan would be the case in the first design. In one embodiment, usefulfor a geothermal power plant operating as in FIG. 1 with ashell-and-tube condenser 6 without a cooling tower “drift” problem, someor all of the boron-rich condensate can be used as makeup to the coolingtower. Alternatively, one or more of the boron-rich fractions can beused as the feed to an evaporative process for producing boric acid. Itwill also be recognized that many of the boron-rich fractions will beoxygen-free when produced in the turbine—and also in the condenser whena surface condenser is employed for condenser 6. These boron-rich butoxygen-free fractions—for example, the boron-rich streams produced inlines 37, 43, and 132 in the geothermal power plant depicted in FIG.1—or the boron-rich fraction captured in line 83 shown in FIG. 6—can beused for various purposes, e.g., as a pump sealant or as a source ofadditional moisture introduced into the main steam supply via line 112for enhancing boron removal in the turbine, or both. Yet anotherpossibility is as a source of make-up for the water introduced via line108 for chloride or other contaminant removal purposes (i.e., steamcleaning). In those geothermal power plants making extensive use of theboron-rich, oxygen-free condensate, it may prove convenient to directmany or all of the boron-rich fractions to a single tank for comminglingand segregation from the boron-lean condensate being produced incondenser 6 for recovery via line 85, the tank then being a source ofoxygen-free boron-containing water for appropriate use throughout theplant.

[0070] In yet another embodiment of the invention, when the geothermalsteam entering the turbine contains ammonia and/or hydrogen sulfide, anyof the methods discussed hereinbefore for capturing and segregatingboron-rich condensate stream(s) will also be useful in capturing some(or all) of the ammonia and/or hydrogen sulfide in correspondingammonia- and/or hydrogen sulfide-rich condensate stream(s). The ammonia,in particular, will rapidly partition into the moisture phase of thesteam, and due to the resulting increase in pH of the moisture, hydrogensulfide will tend more rapidly to dissolve into the moisture phase. Theadvantage of this embodiment of the invention lies most especially withrespect to cooling tower maintenance. That is, because ammonia andhydrogen sulfide are nutrients for microorganisms, the more of each thatis present in steam condensate used as make-up to a cooling tower, thefaster will be the rate at which the cooling tower will become fouledand/or the greater will be the cost in continuously adding biocide inorder to control the fouling. The latter is especially a problem when adirect contact condenser is used and the cycles of concentration arerelatively low, i.e., on the order of 3 to 5. In any event, capturingand segregating ammonia and/or hydrogen sulfide from the steamcondensate used for cooling tower make-up—preferably to the extent ofcapturing and segregating at least 25%, more preferably at least 50%,and most preferably at least 75% of either or both of thecontaminants—will result in substantially reduced cost for biocidesand/or substantially increased time periods between maintenanceshutdowns of the cooling tower for cleaning (with, of course, the costsbeing progressively more decreased and the time periods betweenmaintenance shutdowns being progressively increased with progressivelygreater capture and removal of ammonia and/or hydrogen sulfide). Inaddition, when the geothermal steam is initially relatively low inboron, arsenic, and/or mercury contaminants, to the point that thesegregated ammonia- and/or hydrogen sulfide-rich fractions containingsuch contaminants can be used for agricultural purposes, the segregatedfractions can be used for irrigation purposes not only to water plantsunder cultivation but also to provide a source of nitrogen and/or sulfurnutrients thereto.

[0071] Although the invention has been described above in conjunctionwith the best mode of operation as well as alternative embodiments, itis evident that many other alternatives, modifications, and variationswill be apparent to those skilled in the art in light of the foregoingdescription. For example, the description focused on the threecontaminants of boron, mercury, and arsenic, but the invention islikewise suitable for capturing other contaminants in steam whichreadily partition from the steam phase to the liquid phase uponcondensation of the steam, e.g., as shown above for ammonia. Moreover,even if the geothermal steam under consideration is free of contaminantsor contains contaminants in relatively low concentrations not requiringtheir removal, many embodiments of the invention, e.g., the embodimentshown in FIG. 4, would be useful in producing oxygen-free water for usein those portions of the geothermal power plant where such a liquidwould be of benefit. (For purposes of this invention in all embodiments,a liquid is “oxygen-free” when it contains dissolved oxygen in aconcentration no greater than 100 ppb (0.1 mg/l).) Additionally still,while the focus of the present description has been on geothermal steampassed through a turbine-condenser system, it should be apparent thatthe invention is applicable to any contaminant(s)-containing steamprocessed through a system where an initial or early-produced fractionof the total condensate can be collected and segregated from a laterproduced fraction of the total condensate produced from the steam. (Theterms “total condensate” or “total steam condensate,” as used in thespecification and claims herein, are synonymous and refer to the totalof all liquid water yielded from the system under consideration from wetor dry steam introduced therein.) Accordingly, it is intended to embracein the invention all such alternatives, modifications, and variations asfall within the spirit and scope of the appended claims.

I claim:
 1. A process comprising: (1) introducing geothermal steamcontaining a contaminant selected from the group consisting of boron,mercury, and arsenic into a turbine of a turbine-condenser system; (2)removing from said system a liquid comprising an early-produced,contaminant-rich fraction of total condensate produced in saidturbine-condenser system; and (3) segregating at least some of saidliquid removed in step (2) from said turbine-condenser system, whereinat least some of the total condensate remaining after said earlyproduced fraction is removed in step (2) is neither ultimatelyre-injected into a geothermal formation nor evaporated in a coolingtower system.
 2. A process as defined in claim 1 wherein said liquidremoved in step (2) consists essentially of said early-produced,contaminant-rich fraction, said fraction consisting essentially of aportion of the first 50% of total condensate produced in theturbine-condenser system.
 3. A process as defined in claim 2 whereinsaid portion is less than 15% of the total condensate produced in saidturbine-condenser system.
 4. A process as defined in claim 3 whereinsaid liquid contains more than 50% of at least one of said contaminantsintroduced into the turbine of said turbine-condenser system.
 5. Aprocess as defined in claim 4 wherein said liquid contains condensateproduced in said turbine.
 6. A process as defined in claim 4 whereinsaid liquid consists essentially of condensate produced in said turbine.7. A process as defined in claim 4 wherein said liquid containscondensate recovered on wall surfaces as the steam passes between theturbine and the condenser of said turbine-condenser system.
 8. A processas defined in claim 7 wherein said liquid contains condensate recoveredon wall surfaces as the steam passes through an entryway into saidcondenser.
 9. A process as defined in claim 1 wherein in step (3)essentially all of said liquid removed in step (2) is segregated fromsaid turbine-condenser system.
 10. A process as defined in claim 1wherein the percentage of said total condensate remaining after saidearly produced fraction is removed in step (2) that is neitherultimately re-injected into a geothermal formation nor evaporated in acooling tower system is at least
 5. 11. A process as defined in claim 1wherein the percentage of said total condensate remaining after saidearly produced fraction is removed in step (2) that is neitherultimately re-injected into a geothermal formation nor evaporated in acooling tower system is at least
 10. 12. A process as defined in claim 1wherein the percentage of said total condensate remaining after saidearly produced fraction is removed in step (2) that is neitherultimately re-injected into a geothermal formation nor evaporated in acooling tower system is at least
 15. 13. A process as defined in claim 1wherein the percentage of said total condensate remaining after saidearly produced fraction is removed in step (2) that is neitherultimately re-injected into a geothermal formation nor evaporated in acooling tower system is at least
 20. 14. A process comprising: (1)introducing geothermal steam containing a contaminant selected from thegroup consisting of boron, mercury, and arsenic into a turbine of aturbine-condenser system; (2) removing from said system a liquidcomprising an early-produced, contaminant-rich fraction of totalcondensate produced in said turbine-condenser system; (3) segregating atleast some of said liquid removed in step (2) from saidturbine-condenser system; and (4) removing from the condenser of saidturbine-condenser system a contaminant-lean fraction of totalcondensate, said contaminant-lean fraction being produced later thansaid early produced fraction and having a boron content no greater than2 mg/ l, an arsenic content no greater than 0.05 mg/l, and a mercurycontent no greater than 0.002 mg/l, with said early produced,contaminant-rich fraction containing at least one of boron, arsenic, ormercury in a concentration above the foregoing respective concentrationvalues.
 15. A process as defined in claim 14 wherein some of saidlater-produced fraction is used for make-up to a cooling tower and theproportion of the remainder that is re-injected into a geothermalformation is less than 50%.
 16. A process as defined in claim 14 whereinsaid proportion is less than 25%.
 17. A process as defined in claim 14wherein said proportion is less than 10%.
 18. A process as defined inclaim 11 wherein said proportion is essentially zero.
 19. A processcomprising: (1) introducing geothermal steam containing boron, arsenic,or mercury into a turbine-condenser system in which the steam is passedserially through the turbine and condenser while producing steamcondensate; (2) removing steam condensate containing boron, arsenic, ormercury from the system at one or more locations in theturbine-condenser system where more than 50% of the total steamcondensate has yet to be produced, said removed steam condensateincluding at least some steam condensate recovered after the final stageof said turbine; and (3) preventing at least some of said steamcondensate removed in step (2) from contacting steam and condensate inthe condenser of said turbine-condenser system.
 20. A process as definedin claim 19 wherein said steam condensate in step (2) is removed in aplurality of locations where more than 50% of the total steam condensatehas yet to be produced in the turbine-condenser system.
 21. A process asdefined in claim 19 wherein the total of steam condensate removed instep (2) contains at least 80% of the boron, arsenic, or mercuryintroduced into the turbine.
 22. A process as defined in claim 19wherein said geothermal steam, prior to entry into said turbine of theturbine-condenser system, has been pre-treated by contact with analkaline liquid.
 23. A process as defined in claim 22 wherein saidalkaline liquid comprises ammonium hydroxide.
 24. A process as definedin claim 19 wherein said geothermal steam entering the turbine containsammonia.
 25. A process as defined in claim 19 wherein at least some ofsaid steam condensate in step (2) is removed at a location where morethan 70% of the total steam condensate has yet to be produced in saidturbine-condenser system.
 26. A process as defined in claim 19 whereinat least some of said steam condensate is removed in step (2) at alocation where more than 85% of the total steam condensate has yet to beproduced in said turbine-condenser system.
 27. A process comprising: (1)introducing steam containing a water-soluble contaminant into aturbine-condenser system in which the steam is passed serially throughthe turbine and condenser while producing steam condensate; (2) removingfrom said system an early produced, contaminant-rich fraction of totalcondensate produced in said turbine-condenser system, said fractioncomprising at least 2 percent of the total condensate produced in saidturbine-condenser system; and (3) preventing at least some of said earlyproduced, contaminant-rich fraction removed in step (2) from comminglingin said turbine-condenser system with at least one other fraction of thetotal condensate.
 28. A process as defined in claim 27 wherein saidcontaminant-rich fraction comprises at least 10 percent of the totalcondensate.
 29. A process as defined in claim 27 wherein saidcontaminant-rich fraction comprises at least 15 percent of the totalcondensate.
 30. A process as defined in claim 27 or 28 wherein saidcontaminant-rich fraction comprises less than 30% of the totalcondensate.
 31. A process as defined in claim 27 , 28 , or 29 whereinsaid contaminant-rich fraction comprises less than 25 % of the totalcondensate.
 32. A process as defined in claim 28 or 29 wherein saidcontaminant-rich fraction comprises less than 20% of the totalcondensate.
 33. A process as defined in claim 27 wherein saidcontaminant-rich fraction comprises at least 20 percent but less than 50percent of the total condensate.
 34. A process for reducing the massrate of a contaminant carried in a liquid stream comprising condensaterecovered from a condenser of a turbine-condenser system, wherein thecontaminant was originally present in steam introduced into the turbine,said process comprising (1) removing from said turbine-condenser systema fluid stream containing an early produced fraction comprising at least2 percent of total condensate produced in said turbine-condenser system;and (2) removing from said condenser a liquid stream comprising a laterproduced fraction of total condensate; with said early produced fractionhaving a higher concentration of said contaminant than said laterproduced fraction, and with said liquid stream carrying said contaminantat a total mass rate lower than if said early produced fraction had notbeen removed.
 35. A process as defined in claim 34 wherein condensationin said condenser is accomplished at least in part by direct contact ofsteam with a coolant liquid containing said contaminant, and said liquidstream in step (2) comprises said coolant liquid and said later-producedfraction.
 36. A process as defined in claim 35 wherein said liquidstream contains the contaminant in a concentration lower than for saidcoolant liquid but higher than for said later produced fraction.
 37. Aprocess as defined in claim 34 wherein condensation in said condenser isaccomplished at least in part by direct contact of steam with a coolantliquid containing said contaminant, and said liquid stream removed instep (2) consists essentially of said coolant liquid and saidlater-produced fraction.
 38. A process as defined in claim 34 whereincondensation in said condenser is accomplished at least in part by heattransfer across a solid surface, and said liquid stream removed in step(2) consists essentially of said later produced fraction.
 39. A processas defined in claim 34 wherein said early produced fraction carries saidcontaminant in said fluid stream at a mass rate equal to at least 35% ofthe mass rate at which the contaminant is introduced into said turbine.40. A process as defined in claim 34 wherein said early producedfraction carries said contaminant in said fluid stream at a mass rateequal to at least 50% of the mass rate at which the contaminant isintroduced into said turbine.
 41. A process as defined in claim 34wherein said early produced fraction carries said contaminant in saidfluid stream at a mass rate equal to at least 75% of the mass rate atwhich the contaminant is introduced into said turbine.
 42. A process asdefined in claim 34 wherein said early produced fraction carries saidcontaminant in said fluid stream at a mass rate equal to at least 80% ofthe mass rate at which the contaminant is introduced into said turbine.43. A process as defined in claim 34 wherein essentially none of saidearly produced fraction removed with said fluid stream in step (1) issubsequently commingled with condensate within said condenser.
 44. Aprocess as defined in claim 34 wherein said early-produced fractioncomprises at least 10 percent of the total condensate.
 45. A process asdefined in claim 34 wherein said early produced fraction comprises atleast 15 percent of the total condensate.
 46. A process as defined inclaim 34 , 39 , or 42 wherein said early produced fraction comprisesless than 30% of the total condensate.
 47. A process as defined in claim34 , 40 , 41, or 45 wherein said early produced fraction comprises lessthan 25% of the total condensate.
 48. A process as defined in claim 34 ,41 , 42, or 45 wherein said early produced fraction comprises less than20% of the total condensate.
 49. A process as defined in claim 34wherein said early produced fraction comprises at least 20 percent butless than 50 percent of the total condensate.
 50. A process as definedin claim 1 , 14 , 19, or 27 wherein said steam entering said turbinecontains boron in a concentration of at least 3 ppm by weight or arsenicin a concentration of at least 0.01 ppm by weight.
 51. A process asdefined in claim 1 or 19 wherein said steam entering said turbinecontains boron in a concentration of at least 4 ppm by weight or arsenicin a concentration of at least 0.05 ppm by weight.
 52. A process asdefined in claim 14 or 19 wherein said steam entering said turbinecontains boron in a concentration of at least 5 ppm by weight or arsenicin a concentration of at least 0.25 ppm by weight.
 53. A process asdefined in claim 19 or 27 wherein said steam entering said turbinecontains boron in a concentration of at least 6 ppm by weight or arsenicin a concentration of at least 0.5 ppm by weight.
 54. A process asdefined in claim 1 or 19 wherein said steam entering said turbinecontains boron in a concentration of at least 7 ppm by weight or arsenicin a concentration of at least 0.75 ppm by weight.
 55. A process asdefined in claim 14 or 27 wherein said steam entering said turbinecontains boron in a concentration of at least 8 ppm by weight or arsenicin a concentration of at least 1 ppm by weight.
 56. A process as definedin claim 1 , 14 , 19, or 27 wherein said steam entering said turbinecontains boron in a concentration of at least 9 ppm by weight or arsenicin a concentration of at least 1.5 ppm by weight.
 57. A process forcondensing geothermal steam containing a contaminant selected from thegroup consisting of boron, mercury, and arsenic, the process comprising(1) condensing in a condensing zone a fraction of said geothermal steamto produce a first liquid condensate containing at least one of saidcontaminants in a concentration such that the remaining steam is ofreduced boron, arsenic, or mercury concentration; (2) removing at leastsome of said first liquid condensate from said condensing zone; (3)preventing return of at least some of said removed first liquidcondensate to said condensing zone; (4) condensing in said condensingzone at least some of said remaining steam to produce a second liquidcondensate of lower boron, arsenic, or mercury concentration than forsaid first liquid condensate; and (5) evaporating a substantialproportion but less than 100% of said second liquid condensate in acooling tower system, with at least some of the remainder not beingre-injected into a subterranean formation
 58. A process as defined inclaim 57 wherein a coolant liquid for condensing steam in saidcondensing zone is provided from said cooling tower system.
 59. Aprocess as defined in claim 58 wherein, of the total condensate producedin said condensing zone, the first liquid condensate represents lessthan 15% and the second liquid condensate evaporated in the coolingtower system in step (5) represents at least 70%, with said remainderconstituting the balance and being at least 5%.
 60. A process as definedin claim 57 wherein none of the remainder of said second liquidcondensate is re-injected into a subterranean formation.
 61. A processas defined in claim 57 wherein at least some of the remainder of saidsecond liquid condensate is discharged to the environment.
 62. A processas defined in claim 57 wherein at least some of said second liquidcondensate is used for irrigation purposes.
 63. A process comprising:(1) introducing a steam containing a contaminant into the turbine of aturbine-condenser system; (2) withdrawing steam condensate from theturbine, said steam condensate comprising at least 2% but less than 15%of the total condensate produced in said turbine-condenser system butcontaining more than 25% of said contaminant; and (3) maintaining atleast some steam condensate withdrawn in step (2) separate and apartfrom at least some steam condensate being produced in the condenser ofthe turbine-condenser system.
 64. A process as defined in claim 63wherein said steam condensate withdrawn from the turbine comprises lessthan 10 percent of the total condensate produced in saidturbine-condenser system but contains more than 35 percent of saidcontaminant
 65. A process as defined in claim 63 wherein said steamcondensate withdrawn from the turbine comprises less than 8 percent ofthe total condensate produced in said turbine-condenser system butcontains more than 50 percent of said contaminant.
 66. A process asdefined in claim 63 wherein said steam condensate withdrawn from theturbine comprises less than about 5 percent of the total condensateproduced in said turbine-condenser system but contains more than 65percent of said contaminant.
 67. A process as defined in claim 63wherein said steam condensate withdrawn from the turbine comprises lessthan 5 percent of the total condensate produced in saidturbine-condenser system but contains more than 80 percent of saidcontaminant.
 68. A process as defined in claim 63 , 65 , or 67 whereinsaid steam condensate withdrawn in step (2) comprises steam condensaterecovered from one or more turbine drains associated with said turbine.69. A process as defined in claim 63 , 65 , or 67 wherein said steamcondensate withdrawn in step (2) consists essentially of moisture insteam extracted from the turbine at a location upstream of the finalstage thereof.
 70. A process as defined in claim 14 wherein said earlyproduced, contaminant-rich fraction in said liquid removed in step (2)comprises steam condensate selected from the group consisting of: (a)steam condensate collected on the walls of an entryway of the condenserfrom the turbine; (b) an early produced fraction of steam condensateyielded in said condenser; (c) steam condensate recovered from one ormore turbine drains associated with said turbine; (d) steam condensatein the form of moisture in steam extracted from the turbine at alocation upstream of the final stage thereof; and (e) combinations of(a), (b), (c), and (d).
 71. A process comprising: (1) introducing asteam containing a contaminant into a multi-stage turbine of aturbine-condenser system; (2) withdrawing a fluid stream comprisingsteam and steam condensate from the turbine before the final stagethereof; (3) separating at least some of said withdrawn steam condensatefrom said withdrawn steam; (4) condensing at least some steam exhaustedfrom the final stage of the turbine in the condenser of theturbine-condenser system; and (5) segregating a substantial proportionof said steam condensate separated in step (3) from the condensate inthe condenser of the turbine-condenser system, wherein said steamcondensate withdrawn with said fluid stream in step (2) constitutes atleast 2 percent of total condensate produced in said turbine-condensersystem.
 72. A process as defined in claim 71 wherein the withdrawing ofthe fluid stream in step (2) comprises recovering steam and steamcondensate from turbine drains associated with said turbine.
 73. Aprocess as defined in claim 72 wherein the steam condensate recovered insaid turbine drains comprises less than 10% of the total condensateproduced in the turbine-condenser system but contains more than 25% ofthe contaminant introduced with said steam into said turbine.
 74. Aprocess as defined in claim 72 wherein the steam condensate recovered insaid turbine drains comprises less than 7% of the total condensateproduced in the turbine-condenser system but contains more than 50% ofthe contaminant introduced with said steam into said turbine.
 75. Aprocess as defined in claim 72 wherein the steam contains ammonia as acontaminant.
 76. A process as defined in claim 71 wherein the steamcontains more than one contaminant and said steam condensate withdrawnwith said fluid stream in step (2) constitutes at least 5% of the totalcondensate produced in said turbine-condenser system.
 77. A process asdefined in claim 71 wherein the withdrawing of the fluid streamcomprising steam and steam condensate in step (2) comprises extracting asubstantial proportion of steam containing moisture from the turbine,and step (3) comprises separating said moisture from the extracted steamcontaining moisture and recovering said moisture as the separated steamcondensate.
 78. A process as defined in claim 77 wherein said separatedmoisture comprises less than 10% of the total steam condensate producedin the turbine-condenser system but contains in excess of 20% of saidcontaminant introduced into the turbine with said steam.
 79. A processas defined in claim 77 wherein said separated moisture comprises lessthan 7% of the total steam condensate produced in the turbine-condensersystem but contains in excess of 50% of said contaminant introduced intothe turbine with said steam.
 80. A process as defined in claim 71 , 72 ,or 77 wherein said turbine-condenser system is part of a geothermalpower plant, with geothermal steam being employed to power the turbine.81. A process comprising: (1) introducing geothermal steam containing acontaminant selected from the group consisting of boron, mercury, andarsenic into a turbine-condenser system; (2) removing from said system afluid stream comprising steam and liquid comprising an early-produced,contaminant-rich fraction of total condensate produced in saidturbine-condenser system; (3) separating at sub-atmospheric pressure thesteam from the liquid removed in step (2); and (4) segregating at leastsome of said liquid removed in step (2) and separated in step (3) fromsaid turbine-condenser system.
 82. A process comprising: (1) introducinggeothermal steam containing a contaminant selected from the groupconsisting of boron, mercury, and arsenic into a turbine-condensersystem; (2) removing from said system a liquid comprising anearly-produced, contaminant-rich fraction of total condensate producedin said turbine-condenser system; (3) segregating at least some of saidliquid removed in step (2) from said turbine-condenser system, and (4)recovering from the condenser of said turbine-condenser system aplurality of liquid streams, at least one of which contains boron,mercury, or arsenic in a concentration lower than that of another ofsaid liquid streams.
 83. A process as defined in claim 82 wherein steamcondensed in said condenser undergoes condensation in part due to directcontact with a coolant liquid in a first condensation zone and in partdue to heat exchange across a solid surface with a coolant liquid in asecond condensation zone.
 84. A process as defined in claim 83 whereinat least one liquid stream is recovered in step (4) from each of saidcondensation zones, with at least one liquid stream recovered from thesecond condensation zone having a lower concentration of boron, mercury,or arsenic than for a liquid stream recovered from the firstcondensation zone.
 85. A process as defined in claim 83 wherein at leastone liquid stream is recovered in step (4) from each of saidcondensation zones, with at least one liquid stream recovered from thefirst condensation zone having a lower concentration of boron, mercury,or arsenic than for a liquid stream recovered from the secondcondensation zone.
 86. A process as defined in claim 82 wherein at leastone of the liquid streams recovered in step (4) contains at least two ofboron, arsenic, or mercury in lower concentrations than they arecontained in another of said liquid streams.
 87. A process as defined inclaim 82 wherein at least one of the liquid streams recovered in step(4) contains all three of boron, arsenic, or mercury in lowerconcentrations than they are contained in another of said liquid streams88. A process for removing from geothermal steam a contaminant selectedfrom the group consisting of boron, arsenic, and mercury, said processcomprising contacting said geothermal steam with an aqueous alkalineliquid under conditions removing at least some contaminant from saidgeothermal steam.
 89. A process as defined in claim 88 wherein the pH ofsaid aqueous alkaline liquid is at least 8.0.
 90. A process as definedin claim 88 wherein the pH of said aqueous alkaline liquid is at least8.5.
 91. A process as defined in claim 88 wherein the pH of said aqueousalkaline liquid is at least 9.0.
 92. A process as defined in claim 88wherein the pH of said aqueous alkaline liquid is at least 9.5.
 93. Aprocess comprising: (1) introducing oxygen-free steam into aturbine-condenser system; (2) collecting oxygen-free moisture fromturbine exhaust between the turbine and condenser of saidturbine-condenser system; and (3) directing said oxygen-free moisture toa location external to said turbine-condenser system.
 94. A process asdefined in claim 58 wherein said remainder constitutes a greaterpercentage of the total condensate than the first liquid condensateremoved from said condensing zone in step (2).
 95. A process as definedin claim 58 wherein said remainder constitutes more than twice thepercentage of total condensate than the first liquid condensate removedin step (2).
 96. A process as defined in claim 81 wherein at least someof said separated steam from step (3) is directed into the condenser ofsaid turbine-condenser system, said condenser operatingsubatmospherically.
 97. A process as defined in claim 27 or 34 whereinsaid early produced fraction comprises at least 5% of the totalcondensate produced in said turbine-condenser system.
 98. A process forreducing the concentration of a contaminant selected from the groupconsisting of boron, arsenic, mercury, ammonia, and hydrogen sulfide incirculating water of a cooling tower having as at least one source ofits make-up a steam condensate from a direct contact condensercondensing steam exhausted from a turbine powered with steam containingone or more of said contaminants, said process comprising: (1)collecting an early-produced, contaminant-rich fraction of total steamcondensate produced in the turbine and condenser, said fractionincluding at least some steam condensate recovered after the final stageof the turbine; (2) separating said early-produced, contaminant-richfraction from a steam of reduced contaminant content; (3) condensingsaid steam of reduced contaminant content in said direct contactcondenser; and (4) supplying as a majority of the make-up to saidcooling tower the steam condensate produced in step (3).
 99. A processfor reducing the concentration of a contaminant selected from the groupconsisting of boron, arsenic, mercury, ammonia, and hydrogen sulfide incirculating water of a cooling tower having, as at least one source ofits make-up, a steam condensate from a direct contact condensercondensing steam exhausted from a turbine powered with steam containingone or more of said contaminants, said turbine and condenser forming aturbine-condenser system, said process comprising (1) condensing in saidturbine-condenser system an early-produced, contaminant-rich fraction oftotal steam condensate to produce a steam of reduced contaminantconcentration; (2) removing said early-produced, contaminant-richfraction from said turbine-condenser system; (3) condensing at leastsome of said steam of reduced contaminant concentration in said directcontact condenser; and (4) employing at least some steam condensateproduced in step (3) as make-up to said cooling tower, with at leastsome of the excess of said steam condensate produced in step (3) notbeing evaporated in said cooling tower or injected into a subterraneanformation.
 100. A process as defined in claim 98 or 99 wherein saidsteam powering said turbine comprises geothermal steam and the removed,early produced, contaminant-rich fraction is maintained segregated fromthe turbine-condenser system and the circulating water of the coolingtower.
 101. A process for reducing the concentration of a contaminant inthe drift from a cooling tower, said contaminant originally being ingeothermal steam introduced into a turbine-condenser system, with steamcondensate from the condenser being employed as make-up to said coolingtower, said process comprising removing, in an early-produced fractionof steam condensate from said turbine-condenser system, sufficient ofsaid contaminant originally present in said geothermal steam so as toreduce the concentration of said contaminant in water circulating insaid cooling tower by at least 10%.
 102. A process as defined in claim99 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 20%.
 103. A process as definedin claim 98 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 30%.
 104. A process as definedin claim 99 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 40%.
 105. A process as definedin claim 98 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 50%.
 106. A process as definedin claim 99 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 60%.
 107. A process as definedin claim 98 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 70%.
 108. A process as definedin claim 99 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 80%.
 109. A process as definedin claim 98 or 101 wherein the concentration of said contaminant in saidcirculating water is reduced by at least 90%.
 110. A process as definedin claim 98 , 99 , or 101 wherein said contaminant comprises boron. 111.A process as defined in claim 98 , 99 , 101 wherein said contaminantcomprises arsenic.
 112. A process as defined in claim 98 , 99 , 101wherein said contaminant comprises ammonia.
 113. A process as defined inclaim 98 , 99 , 101 wherein said contaminant comprises hydrogen sulfide.114. A process as defined in claim 98 , 99 , 101 wherein saidcontaminant comprises mercury.
 115. A process as defined in claim 98 ,99 , or 101 wherein the boron content of the circulating cooling towerwater is maintained at no greater than 2 mg/l, an arsenic content nogreater than 0.05 mg/l, and a mercury content no greater than 0.002mg/l.
 116. A process as defined in claim 1 , 27 , 98, 99, or 101 whereinsteam entering said turbine comprises boron present in a concentrationof at least 10 ppm by weight, arsenic in a concentration of at least 2.0ppm by weight, or mercury in a concentration as to be detectable inliquid in the condenser.
 117. A process as defined in claim 1 , 98 , or101 wherein steam entering said turbine comprises boron present in aconcentration of at least 11 ppm by weight or arsenic in a concentrationof at least 2.5 ppm by weight.
 118. A process as defined in claim 1 , 27, or 98 wherein steam entering said turbine comprises boron present in aconcentration of at least 13 ppm by weight or arsenic in a concentrationof at least 3 ppm by weight.
 119. A process as defined in claim 1 , 27 ,71, 98, 99, or 101 wherein steam entering said turbine comprises boronpresent in a concentration of at least 15 ppm by weight or arsenic in aconcentration of at least 4 ppm by weight.
 120. A process for condensinggeothermal steam containing a contaminant selected from the groupconsisting of boron, arsenic, mercury, ammonia, and hydrogen sulfide,the process comprising (1) condensing a fraction of said geothermalsteam to produce a liquid condensate containing sufficient contaminantthat the remaining steam is of reduced contaminant concentration, saidfraction containing condensate recovered from a steam entryway area of acondenser; (2) removing at least some of said liquid condensate fromsaid remaining steam of reduced contaminant concentration; and (3)condensing in said condenser at least some of said remaining steam ofreduced contaminant content in the absence of contact with the steamcondensate removed in step (2).
 121. A process as defined in claim 27 ,34 , 63, or 71 wherein said contaminant is selected from the groupconsisting of boron, mercury, arsenic, ammonia, and hydrogen sulfide.122. A process comprising: (1) introducing geothermal steam containing acontaminant selected from the group consisting of boron, mercury,arsenic, ammonia, and hydrogen sulfide into a turbine of aturbine-condenser system; (2) removing from said system a liquidcomprising an early-produced, contaminant-rich fraction of totalcondensate produced in said turbine-condenser system; and (3)segregating at least some of said liquid removed in step (2) from saidturbine-condenser system, wherein at least some of the total condensateremaining after said early produced fraction is removed in step (2) isdischarged to the environment.
 123. A process as defined in claim 122wherein the remaining total condensate discharged to the environment isused for irrigating plants under cultivation.
 124. A process comprising:(1) introducing geothermal steam containing boron, arsenic, mercury,ammonia, or hydrogen sulfide into a turbine-condenser system in whichthe steam is passed serially through the turbine and condenser whileproducing steam condensate; (2) removing steam condensate relativelyrich in boron, arsenic, mercury, ammonia, or hydrogen sulfide from thesystem at one or more locations in the turbine-condenser system wheremore than 50% of the total steam condensate has yet to be produced, saidremoved steam condensate including at least some steam condensaterecovered after the final stage of said turbine; and (3) preventing atleast some of said steam condensate removed in step (2) from contactingsteam and condensate in the condenser of said turbine-condenser system.125. A process as defined in claim 122 or 124 wherein said contaminantis selected from the group consisting of ammonia and hydrogen sulfide.126. A process for condensing steam containing a contaminant in acondenser, the process comprising (1) condensing a first fraction ofsaid steam in a first portion of the condenser so as to produce (a) acontaminant-rich fraction of total condensate produced from said steamin said condenser and (b) a remaining steam of reduced contaminantconcentration; (2) collecting a first liquid comprising saidcontaminant-rich fraction of total condensate in said first portion ofsaid condenser; (3) introducing said remaining steam into a secondportion of said condenser; (4) condensing a substantial proportion ofsaid remaining steam in said second portion of said condenser so as toproduce a contaminant-lean fraction of total condensate; (5) collectinga second liquid comprising said contaminant-lean fraction of totalcondensate in said second portion of said condenser, with said first andsecond liquid being segregated from each other in said condenser; and(6) separately removing from said condenser said first and secondliquids.
 127. A process comprising: (1) introducing steam containing oneor more water-soluble contaminants and one or more non-condensable gasesinto a turbine of a turbine-condenser system; (2) withdrawing from saidturbine prior to the final stage thereof steam containing (a) moisture,said moisture being rich in at least one of said contaminants, and (b)at least some of said one or more non-condensable gases; (3) separatingsaid moisture from said steam; (4) separately recovering from step (3) aliquid comprising said moisture and steam containing said one or morenon-condensable gases; (5) condensing in said condenser steam exhaustedfrom said turbine to produce a steam condensate contaminant-lean ascompared to said moisture; and (6) removing from said condenser one ormore non-condensable gases by means including a steam ejector employingsteam recovered in step (4).
 128. A continuous process comprising: (1)continuously adding liquid water to superheated steam introduced into aturbine of a turbine-condenser system, said superheated steam containinga contaminant; (2) removing from said system a liquid comprising anearly-produced, contaminant-rich fraction of total condensate producedin said turbine-condenser system, said fraction containing at least somemoisture produced in said turbine; and (3) segregating at least some ofsaid liquid removed in step (2) from said turbine-condenser system. 129.A process as defined in claim 126 , 127 , or 128 wherein saidcontaminant is selected from the group consisting of boron, mercury,arsenic, ammonia, and hydrogen sulfide.
 130. A process for reducing theconcentration of a contaminant in the circulating water in a coolingtower, said contaminant originally being in geothermal steam introducedinto a turbine-condenser system, with steam condensate from thecondenser being employed as make-up to said cooling tower, said processcomprising removing, in an early-produced fraction of steam condensatefrom said turbine-condenser system, sufficient of said contaminantoriginally present in said geothermal steam so as to reduce theconcentration of said contaminant in water circulating in said coolingtower by at least 15%.
 131. A condenser comprising (1) a first chamberhaving an entryway for a vapor to be condensed; (2) means for collectingliquid within said first chamber; (3) a second chamber having anentryway communicating with said first chamber for recovering vapor notcondensed in said first chamber; (4) means for condensing vapor in saidsecond chamber by heat exchange across a surface with coolant fluid; (5)means for collecting liquid condensate in said second chamber separateand apart from liquid collected in said first chamber; and (6) means forintroducing a coolant fluid, including coolant fluid exiting fromsurface condensing means (4), into said first chamber to causecondensation of vapor therein by direct contact heat exchange with thecoolant fluid.
 132. A condenser comprising (1) a first chamber having anentryway for a vapor to be condensed; (2) means for collecting liquidwithin said first chamber; (3) means for condensing vapor in said firstchamber by heat exchange across a surface with coolant fluid; (4) asecond chamber having an entryway communicating with said first chamberfor recovering vapor not condensed in said first chamber; (5) means forcollecting liquid condensate in said second chamber separate and apartfrom liquid collected in said first chamber; and (6) means forintroducing a coolant fluid exiting from surface condensing means (3)into said second chamber to cause condensation of vapor therein bydirect contact heat exchange with the coolant fluid.
 133. A condensercomprising: (1) a housing holding a first chamber and a second chamber,the first chamber having an entrance for a vapor to be condensed, thefirst chamber being separated from the second by a plurality of wallbarriers arranged to provide vapor communication between the chambers bya tortuous path and to separate essentially all liquid collected in thefirst chamber from essentially all liquid collected in the secondchamber, with each chamber having one or more openings for collectedliquid to exit therefrom without contacting liquid collected in theother chamber; (2) a surface heat exchanger within said second chamberfor causing condensation of vapor in said second chamber by heatexchange with a coolant introduced into said surface heat exchanger froma source external to the condenser; and (3) a fluid communication systemfor introducing a fluid coolant comprising the fluid coolant exitingsaid surface heat exchanger into said first chamber to causecondensation of vapor therein by direct contact heat exchange.
 134. Anapparatus comprising (1) a steam-powered turbine; (2) a condenser forcondensing steam exhausted from said turbine; (3) a fluid communicationsystem between said turbine and condenser for directing steam exhaustedfrom the turbine to said condenser; (4) means, within said fluidcommunication system, for collecting moisture from steam passingtherethrough; and (5) means for directing said collected moisture to alocation external to the turbine, condenser, and fluid communicationsystem.
 135. A turbine-condenser system for processing contaminatedsteam introduced into the turbine, comprising (1) a turbine-condensersystem; (2) means, located between the final stage of said turbine andthe entryway area of the condenser, for collecting moisture from saidsteam and (3) means for segregating the collected moisture from at leastthe majority of the steam condensed in the condenser.
 136. The system ofclaim 135 wherein said means (2) comprises means for collecting moistureaccumulating on wall surfaces and means for enhancing the accumulationof moisture on said wall surfaces.
 137. A condenser having an entrywayfor vapors to be condensed, said entryway having means for collectingcondensed vapors on the walls thereof prior to said condensed vaporsreaching the lowest point in said condenser for liquid to gather, withsaid entryway further having means for removing said collected condensedvapors from said condenser without said collected vapors comminglingwith the majority of vapors condensed in said condenser.
 138. Anapparatus comprising in fluid communication: (1) a turbine-condensersystem; (2) means for withdrawing steam from said turbine at aninterstage location therein; (3) means for removing moisture from steamwithdrawn by means (2); (4) a steam ejector for removing non-condensablegases from said condenser; and (5) means for removing moisture-freesteam from means (3) and directing said moisture free-steam to powersaid ejector.